Blood flow from the left ventricle to the aorta is regulated by the aortic valve which may be tricuspid (normal) or bicuspid (pathologic). As the description suggest, the valve may include three crescent-shaped leaflets, or two leaflets, that each move between a closed position where blood cannot pass and an open position where blood can pass. In the closed position, the margins of the leaflets come together flushly to seal the passage between the left ventricle and the aorta. In the open position, each of the leaflets moves into a cavity, termed a sinus of Valsalva, allowing blood to flow through the valve orifice. Two of the sinuses include coronary ostia for the right and left coronary arteries. Because the third sinus does not contain an ostia, it is referred to as the non-coronary sinus.
Malfunction of the aortic valve can have severe clinical consequences. Replacement of the aortic valve is typically used in patients who have either or both a leakage or obstruction of the aortic valve. These conditions may result from a congenital defect or from a disease condition such as a degenerative calcification or inflammation of the aortic valve. Fortunately, surgical procedures and prostheses have been developed for replacing defective aortic valves. These procedures may involve excision of the sinuses of Valsalva and reattachment of the coronary arteries to the prosthesis at a convenient location if the ascending aorta is also involved with pathologic changes. While aortic valve replacement is usually successful, the results may be less than ideal long-term because of removal of the sinuses of Valsalva and suboptimal placement of the coronary artery anastomoses can have a negative effect on the fluid dynamics of blood flow.
Other conditions can affect the ascending aorta. For example, in Marfan's syndrome, a dilation of the aortic root (the area where the aorta meets the aortic valve) is often observed in patients. This can dilate the aortic valve, causing it to leak. Aneurysms can also occur on the aorta and sinuses of Valsalva. Treatment of these conditions may require removal and replacement of the ascending aorta while leaving the aortic valve in place.